This invention is related to a pressure control device employed in antiskid brake control devices for automotive vehicles.
Of the various antiskid devices, an example of an unitized magnetic valve type aimed at reducing the manufacturing cost, is disclosed in JPA, First Publication, S59-32548. This device, as shown in FIG. 2, includes: a main fluid path 83, for transmitting the brake liquid pressure, disposed between a master cylinder 81 and a wheel cylinder 82; and a bypass path 84 branching from the main path. In the bypass path 84, there are normally closed (n/c) electro-magnetic valve 85 which open on reducing brake pressure, and allows the brake fluid in the main path 83 to enter the bypass path 84; and a reservoir 86 for storing the brake fluid which flows in through the n/c electro-magnetic valve 85; and a pumping device 87 which returns the brake fluid in the reservoir 86 to the main path 83 while keeping the n/c electro-magnetic valve 85 closed, which is disposed to the opposite side of the reservoir 86. There is a normally open (n/o) valve 88, disposed between the master cylinder 81 and the junction of the main path 83 and the master cylinder 81 side of the bypass path 84, which closes when the fluid flows into the bypass path 84. The pumping device 87 includes: a pump 89 which pumps and discharges the fluid; a one-way suction valve 90 which is disposed between the reservoir 86 and the pump 89, and allows the fluid flow from the reservoir 86 only; and a one-way discharge valve 91 which is disposed between the pump 89 and the main path 83, and allows the fluid flow to the main path 83.
During the operation of the antiskid control device, the device performs appropriate alternating operations of reducing the fluid pressure to the wheel cylinder 82 and increasing the fluid pressure to the main path 83: by opening the n/c electro-magnetic valve 85 and permitting the fluid in the main path 83 to flow into the bypass path 84 and, at the same time, closing the n/o valve 88 disposed on the master cylinder 81 side, so as to perform the fluid pressure reduction operation to the wheel cylinder 82 (the pump 89 is non-active at this time); and by closing the n/c electro-magnetic valve 85 in the bypass path 84, and at the same time, activating the pump 89 to pump the fluid from the reservoir 86 through the one-way valve 90 and discharges the fluid into the main path 83, through the one-way discharge valve 91 so as to perform the fluid pressure increase operation. To perform such a cyclic operations delicately, it is possible to resort to a pressure holding action preventing the pressure from rising by temporarily stopping the operation of the pump 89 during the pressure increase phase.
However, in a brake pressure adjustment device of such a construction, there is a time delay in the control action of the pump to generate decreasing, holding and increasing phases of the fluid pressure, because of the inertial effects associated with the mass of the pump.